1. Field of the Invention
This invention relates to improvements in an oil pressure circuit in a starting clutch for use in an automatic transmission for a vehicle or the like.
2. Related Background Art
As a device located intermediately of an engine and an automatic transmission body, there is known a starting clutch in which one of a torque converter with a lock-up clutch and a clutch piston is controlled by oil pressure and the clutch piston is controlled by a coil spring or the like.
The torque converter with a lock-up clutch cannot be neutrally controlled by itself. Specifically it cannot completely cut off the transmission of power.
In contrast with this is a starting clutch that is located intermediately of an engine and an automatic transmission and that controls the clutch piston by the use of an urging force from oil pressure on the one hand and by an urging force from the reaction force or the like of a coil spring on the other hand. When, in this starting clutch, oil pressure is used for the fastening (engaging) control of the clutch piston, necessary pressure can be supplied with good responsiveness. But when the reaction force of the coil spring is used for the liberating (releasing) control of the clutch piston, it is impossible to vary the set reaction force in itself. Also, in designing, the reaction force for the liberation of the coil spring is usually set to a considerably low value relative to the fastening oil pressure to thereby make the fastening force (=&lt;oil pressure for fastening&gt;-&lt;reaction force of the coil spring&gt;) great.
When the reaction force of the coil spring is set to a low value relative to the oil pressure, even if a clutch piston control valve is in its liberated state, the clutch piston does not actually begin to be liberated, in the process wherein the clutch piston changes from its fastened state to its liberated state, until the fastening pressure drops below the reaction force of the coil spring. That is, even if the clutch piston control valve is in its liberated state, the delay until the fastening pressure becomes below the reaction force of the coil spring retards the timing of clutch liberation, thus resulting in the problem that the shock during the clutch fastening or the amount of transmission of necessary torque cannot be adjusted. Even when the reaction force of the coil spring is provided for the clutch piston fastening and oil pressure is provided for the clutch piston liberation, the delay of the reaction force of the coil spring retards the timing of the clutch fastening as in the aforedescribed case, thus causing various problems.
FIG. 1 of the accompanying drawings is a schematic cross-sectional view showing an example of the prior-art starting clutch for location intermediately of the engine and the automatic transmission, wherein the fastening movement of the clutch piston is effected by oil pressure and liberating movement of the clutch piston is effected by the reaction force of the coil spring.
The starting clutch 100 comprises an input shaft 101 having an axially extending hole and provided with a radially extending hole 122, a fixed shaft 102 provided outside the input shaft 101 and provided with a radially extending hole 118, and a sleeve 103 provided outside the fixed shaft 102. The sleeve 103 is a portion of a housing 104, and a clutch case 105 for the starting clutch 100 is mounted in the housing 104. The clutch case 105 rotates with the housing 104.
A clutch piston 106 is axially slidably disposed in the clutch case 105. A plurality of plates 116 axially slidable through a spline or the like are axially provided at predetermined intervals on the outer peripheral cylindrical portion 107 of the clutch case 105. Also, a fixed plate 108 is fixed to the clutch case 105 outside the plates 116. Also, a projected portion 109 is provided on the back of the housing 104.
A radially outwardly extending flange portion 111 is provided on the inner peripheral cylindrical portion 110 of the clutch case 105, and a coil spring 112 is disposed between the flange portion 111 and the clutch piston 106. The coil spring 112 gives a force in a direction to urge the clutch piston 106 against the inner peripheral surface of the clutch case 105. Further, the inner peripheral cylindrical portion 110 of the clutch case 105 is formed with a radially extending hole 119.
The end portion of the input shaft 10.1 of the starting clutch 100 provides a disc-like hub 113 on the rear side of the housing 104, and an axially extending cylindrical portion 114 is provided radially outwardly of the hub 113 in opposed relationship with the input shaft 101.
A plurality of friction plates 115 of the starting clutch 100 are axially slidably provided at predetermined intervals in the axial direction on the cylindrical portion 114 of the hub 113 through a spline or the like.
The oil path of the starting clutch 100 will now be described. A drain oil path D for cooling oil for cooling the friction surfaces of friction plates 116 having a drain exit 117 between the sleeve 103 and fixed shaft 102 of the starting clutch and the plates 115 is formed between the fixed shaft 102 of the starting clutch 100 and the sleeve 103 of the starting clutch 100.
Likewise, an operating oil path E for operating the clutch piston 106 communicates with the gap 120 between the fixed shaft 102 and the input shaft 101 through a hole 118 in the final shaft and a hole 119 in the inner peripheral cylindrical portion 110 of the clutch.
Further, in communication with a through-aperture 121 in the input shaft 101, there is formed a cooling oil path F for cooling the friction surfaces of the friction plates 115 and plates 116 through a hole 122.
There are a plurality of communication holes 123 in the outer peripheral cylindrical portion 107 of the clutch case 105, and there are provided a plurality of communication holes 124 in the outer peripheral cylindrical portion 114 of the hub 113, and they communicate the drain oil path D and the cooling oil path F with each other through the gaps between the friction plates 115 and the plates 116. The drain oil path D and the cooling oil path F together constitute an oil path exclusively for cooling the friction surfaces.
Description will hereinafter be made of the flow in the friction surface cooling oil path of the prior-art starting clutch 100 of the above-described construction.
The cooling oil passes through the cooling oil path F, i.e., from the through-aperture 121 in the input shaft to the hole 122, toward the friction surface of the starting clutch 100, and flows in a direction to lubricate, i.e., cool, the friction surfaces. This cooling oil flows from the communication holes 123 to the drain exit 117 and is discharged.
If a friction material attached on the friction plates 115 is formed with grooves extending, for example, from the radially inner periphery side to the outer periphery side of the friction material and extending through the friction material, the flow of the cooling oil will become smoother and there will be obtained a greater cooling effect. The number of the grooves can be arbitrarily set, but a plurality of such grooves may preferably be provided in the circumferential direction for the purpose of the smooth flow of the cooling oil.
In contrast, the operating oil path E in the clutch piston 106 of the starting clutch 100 is such that the operating oil flows from the gap 120 between the fixed shaft 102 and the input shaft 101 and through the hole 118 and the hole 119 to thereby raise the oil pressure in an oil pressure chamber 125 and move the clutch piston 106 leftwardly as viewed in FIG. 1 by the oil pressure force. As a result, the friction plates 115 and the plates 116 are fastened to (engaged to) each other between the clutch piston 106 and the fixed plate 108, and the starting clutch 100 becomes fastened and the transmission of power becomes possible. Next, if the oil pressure in the oil pressure chamber 125 is decreased, the clutch piston 106 is rightwardly moved by the reaction force of the coil spring 112 and the friction plates 115 and the plates 116 are separated from each other, and the fastened state of the starting clutch 100 is released and the starting clutch becomes unfastened (disengaged).
Here, the power transmitting route in the prior-art starting clutch will be described. During the fastening of the starting clutch, the power outputted from an engine, not shown, is transmitted to the housing 104 through a drive plate, not shown, and through the projected portion 109 of the housing 104. Next, the power is transmitted to the clutch case 105 of the starting clutch which rotates with the housing 104, and is transmitted to the input shaft 101 of the starting clutch 100 through the plates 116 connected to the clutch case 105 through a spline or the like, and the friction plates 115 and hub 113 urged against the plates 116 by the clutch piston 106. The power transmitted to the input shaft 101 is transmitted to an automatic transmission body, not shown.
Next, during the liberation (release) of the starting clutch 100, the power output from the engine is transmitted to the housing 104 through the drive plate and through the projected portion 109 of the housing 104. Thereafter, the power is transmitted to the clutch case 105 of the starting clutch which rotates with the housing, and is transmitted to the plates 116 connected to the clutch case 105 through a spline or the like. During the liberation of the starting clutch 100, however, the connection between the plates 116 and the friction plates 115 is cut off and therefore, there is no transmission of the power from the plates 116 to the friction plates 115 and the starting clutch 100 assumes a neutral state.
In the prior-art starting clutch described above, when the clutch piston is to be operated by the use of the reaction force of the coil spring, the piston cannot be operated unless the opposing oil pressure becomes below the reaction force of the coil spring. Moreover, the difference between the force Of the coil spring and the force of the fastening oil pressure urging the clutch piston is used as the clutch piston urging force necessary for the fastening of the clutch. Therefore, even if the reaction force (urging force) of the coil spring is strengthened, the fastening oil pressure also becomes higher so that greater pump power is required.